Pressure intensifier



1959 1. s. HOUVENER 2,897,762

PRESSURE INTENSIFIER Filed Dec. 20, 1956 v 4 Sheets-Sheet 1 I 1 4 INVENTOR. N N I Lew/v6 5. hauvewsg BY W, mrm

A rramvzvi 1. s. HOUVENER 2,897,762

4 Sheets-Sheet 3 PRESSURE INTENSIFIER flea/1N6 5. Had Via/EB BY AIM [II-42 M22 Air-re al!!! Aug. 4, 1959 Filed Dec. 20, 1956 United States Patent'Ofiice 2,897,762 PRESSURE INTENSIFIER Irving S. Houvener, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Application December 20, 1956, Serial No. 629,670

15 Claims. (Cl. 103-52) This invention relates to improvements in pressure intensifiers.

While the device of the present invention is particularly adapted for use in intensifying the pressure of fracturing fluids used in oil Well drilling technique, the intensifier is adaptable for a variety of pressure intensifying and motion transmitting purposes.

An important feature of the intensifier of the present invention is the concentric arrangement of the high pressure chamber within the low pressure chamber. Accordingly, if the high pressure chamber bursts, the explosive force thereof will be absorbed and contained by the low pressure fluid and its chamber. Danger to personnel and property from this source is correspondingly lessened. Moreover, leakage from the high pressure chamber is intercepted by and contained within the low pressure chamber.

The intensifier of the present invention is capable of exerting extremely high pressure on a fluid subject only to the strength of materials used in its fabrication. For oil well treating purposes (e.g., hydraulically fracturing the producing formation of a producing well, or input formation of a disposal well), however, the intensifier is designed to pressurize the well treating fluid (erg, oil, water) to about 12,000 to 15,000 p.s.i. While the in tensifying ratio of the device is variable in a wide range according to the specific dimensions thereof, I have found that for well treating purposes, for example an intensification ratio of about six to one is desirable where the low pressure Working fluid delivered to the intensifier from the primary power source is available at about 2,000 to 2,500 p.s.i. and 1,000 to 1,500 g.p.m.

The device of the present invention is adapted to pressurize the pumped fluid (e.g., well treating fluid) at a flow rate higher than is possible in any intensifying device commercially available. While prior art pressure intensifiers are capable of pressurizing the pumped fluid to 12,000 p.s.i., their flow rate is low as compared to the intensifier of the present invention. While my intensifier can supply pumped fluid at a rate of about five barrels per minute, it has heretofore been commercially impossible to safely achieve flow rates in excess of about two to four barrels per minute with pumps of equal hydraulic horsepower.

The intensifier of the present invention is double acting in a balanced structure and hence reduces fluid and mechanical shock characterizing prior art intensifiers.

Other features and advantages of the present invention will be more apparent to one skilled in the art upon an examination of the following disclosure in which:

Fig. 1 is a diagrammatic view showing plural intensifiers according to my invention, connected in a fluid circuit in which they may be used to intensify the pressure of pumped or fracturing fluid as supplied to an oil Well, for example.

Fig. 2 is a perspective view partly cut away and in cross section showing dual intensifiers according to my in- 2,897,762 Patented Aug. 4, 1959 vention and their fluid connections to a control valve mechanism.

Fig. 3 is a fragmentary axial cross section taken througha pressure intensifier embodying the present invention.

Fig. 4 is a cross section taken along the line 4--4 of Fig. 3.

Fig. 5 is a fragmentary cross section taken along the line 55 of Fig. 4.

Fig. 6 is a greatly enlarged axial cross section through a typical check valve which controls the admission and discharge of pumped fluid from an isolator chamber of the intensifier.

Fig. 7 is a cross sectional view taken along the line 77 of Fig. 6 and showing the patterned facing of the valve.

Fig. 8 is an axial cross section taken through a preferred isolator piston used in the device of the invention.

Fig. 9 is a cross section taken along the line 9-9 of Fig. 7.

In the well treating art it is conventional to fracture a formation extending laterally from a well bore to open up the formation and encourage flow of the desired fluid, e.g., oil therealong and up the well bore. The earth formations penetrated by the well bore may be fractured by pumping into the well bore a relatively dense and heavy fracturing fluid mixture which is usually sand in liquid suspension. In the case of oil wells, the liquid is preferably oil and is recovered when the well produces, although water may be used.

Depending on the overburden, the fracturing mixture is placed under a pressure which may need to be as high as 12,000 to 15,000 p.s.i. or more. At some pressure which will exceed the overburden and the strength of the formation, the earth formation will fracture and cracks will be formed therethrough through which earth fluids, e.g., oil, may flow to the Well bore.

As shown in Fig. l the fracturing or pumped fluid 13 may be stored in a tank 11. One or more booster pumps, e.g., the series 12, may be employed to raise the pressure of the fluid 13 to be pumped to several thousand p.s.i. For relatively light overburdens one or more of the pumps 12 may be capable of raising the pressure of the fluid 13 sufliciently high for fracturing purposes. Ordinarily, however, pumps 12 need not deliver fluid at any pressure above 4,500 p.s.i.

When the pumps 12 have adequate pressure capacity, fluid 13 is delivered directly to the well head 10 through hydraulic fluid lines 14 and 15 and through the cutoff valve 16 and control valve 17. Where higher pressures are needed, however, valve 16 may be closed. Fluid 13 then is routed through hydraulic lines 21, 22 to the pressure intensifier apparatus which increases the pressure of the fluid 13 and supplies it to the well head 10 through fluid lines 23, 24 and control valve 17.

In the diagrammatic illustration of Fig. l, fluid supply line 22 may branch at 25 to supply the isolator chambers 26, 27 at corresponding ends of dual pressure intensifiers 28, 29. Another branch line 32 may supply isolator chambers 33, 34 at corresponding opposite ends of the pressure intensifiers 28, 29.

The respective intensifiers 28, 29 have a primary circuit for relatively low pressure working oil or other suitable fluid 35 stored in tank 36. The low pressure working fluid is pressurized in the particular embodiment illustrated by pump 37 to about 2,000 to 2,500 p.s.i. or other suitable pressure and supplied through line 32 valve 38 and fluid lines 41, 42, 43, 44 to the low pressure fluid chambers of the intensifiers 28, 29. Spent low pressure Working fluid will return to tank 36 through the line 45.

The intensifiers 28, 29 have contained therewithin captive high pressure oil or other suitable fluid 46 within the high pressure chambers thereof. This high pressure captive fluid, e. g., oil, is desirably the same liquid as the liquid 35. It is uncontaminated by sand or other solids of the mixture to be injected into the well which might score the cylinders of the intensifier and is isolated from the fluid 13 which is to be pumped by the isolator pistons 47 in the respective isolator chambers 26, 2'7, 33, 34. As will hereinafter appear, measured small quantities of high pressure captive fluid 46 are periodically flushed through and past the pistons 47 to commingle with the pumped fluid, such flushing desirably occurring when the isolator pistons reach the end of their strokes.

The specific structure of the respective intensifiers is shown in perspective in Fig. 2 and in cross section in Figs. 3 and 5. Each intensifier 28, 29 comprises an outer low pressure fluid cylinder 50 having end heads 49, 51 held in assembly with the cylinder 50 by the clamp bolts 52. Within the cylinder 50 are fluid displacement members including a freely reciprocating or floating piston 53. In the embodiment of the invention shown in this application and as best shown in Fig. 4, piston 53 may be provided with plural axial bores, preferably four innumber. Two diametrically aligned bores 54 open to face 55 of piston 53 and are closed with respect to the opposite face 56 thereof to form cylinders within the piston 53. The other two diametrically aligned bores 57 open to face 56 of the piston and are closed to face 55 to form additional cylinders within piston 53.

Additional fluid displacement members are fixed with respect to the cylinder and are mounted for relative reciprocation within the bores of piston 53. In end head 49 two tubes 68 are fixed by the threaded couplings shown at 59. The tubes 68 extend axially of the cylinder 50 and are received within the bores 54 of piston 53. End head of the cylinder 58 is similarly provided with paired tubes 62 which extend axially of the cylinder 50 and are received within the bores 57 of floating piston 53. The re spective tubes 60, 62 are hollow for communication between the respective piston bores 54, 57 through the end heads 49, 51 and the isolator chambers 26, 27, 33, 34 of the respective intensifiers. The exposed or effective area of the respective faces 55, 56 of the floating piston 53, in the particular embodiment of the invention illustrated, is six times the effective area of each pair of tubes 68, 62.

Low pressure working fluid 35 is admitted to cylinder 50 at opposite sides of the floating piston 53 through ports 63, 64, 65, 66 which respectively connect to fluid lines 44, 42, 43, 41. In Fig. 2 these fluid lines are illustrated only diagrammatically by arrows.

As best shown in Fig. 3 the respective isolator chambers 26, 27, 33, 34 are connected to the end heads 49, 51 by means of the threaded couplings 67. In the preferred embodiment of the invention the respective chambers 26, 37, 33, 34 have cylinder linings 68 on which the isolator pistons 47 are free to reciprocate. The preferred form of isolator piston is shown in Fig. 8, an alternate form being suggested in Fig. 2. 7

As shown in Fig. 8 piston 47 comprises a spool having flanges 71, 79 grooved medially at 72 to receive sleeve 70 on which the chevron type packing rings '73 are disposed. The packing rings 73 are held under axial pressure by the compression spring 74 which bears between the packing rings 73 and the guide fins 75 which project from the flange 79 to the same diameter as the packing rings '73. The chevrons 73 are arranged as shown to permit fluid in chambers 26, 27, 33, 34, respectively, to bypass the piston from the high to the low pressure side. The guide fins 75 help stabilize the reciprocating movement of the piston along cylinder wall lining 68, as in Fig. 3.

Piston flange 71 may be provided with pressure relief by pass ports 76 normally closed by annular valve plate 77 which is under pressure of the compression spring 78 which bears against the opposed flange 79 of the piston. Flange 79 is also provided with bypass ports 82 to pass the fluid admitted through ports 76.

In Fig. 2 a somewhat different embodiment of isolator piston 47 is suggested. It may consist simply of a block of rubber or like elastomer. having a grooved periphery to form chevron type packing ribs engaged with the walls of the isolator chamber.

The specific isolator structure is broadly immaterial. Under some circumstances a rubber diaphragm could be used to isolate the captive high pressure fluid from the fluid to be pumped. However, because of the stresses to which the isolator member may be subject, I prefer the specific form shown in Fig. 8 which will resist-both mechanical and hydraulic shock.

The pumped or fracturing fluid is admitted to and released from the isolator chambers 26, 27, 33, 34 by the check valve mechanism shown in detail in Figs. 3 and 6. Here again the specific check valves used are broadly immaterial. Simple ball valves would be satisfactory in'some circumstances. However, to deal with the granular foreign matter, suspended in the pumped or fracturing fluid as in well treating applications, the specific valves shown in Figs. 3 and 6 are preferred.

The respective insolator chambers may be reduced in cross section at 83 and a duct 84 is formed therethrough which communicates with the passage 85 in check valve housing 86.

The inlet fluid line 25 is connected through valve housing inlet head 87 which communicates with check valve 88'. The outlet fluid line 23 is connected to valve housing outlet head 91 which communicates with check valve 92. The respective valves 88, 92 are biased by their springs 93 to closed position.

The specific valves 88, 92 are shown in detail in Fig. 6. The valve seat 94 is desirably conical. The valve is provided with a face 95 which desirably comprises an elastomer such as natural or synthetic rubber. Neoprene or buna-N have been found to make suitable valve faces. The elastomer face may mold itself about the gritty foreign matter present in the pumped fluid to make good contact with seat 94.

Moreover, the seating face of the valve facing 95 is desirably patterned to provide alternate coplanar ribs 97 and grooves 96 as best shown in Figs. 7 and 9. The grooves 96 provide pockets in which gritty foreign matter may lodge during the seating operation of the valve. The high points on the ridges 97 may sweep foreign matter into the grooves 96, thus leaving the ridges free and clear for intimate contact with the seat 94. A regular wafile pattern as shown in Fig. 7 is preferred for the valve facing, although it is clear that any comparable pattern providing ridges and grooves would have utility in the device of my invention.

The valve seat 94 may be threaded at 98 to the valve casing 86. The seat 94 is provided with a cylindrical wall portion 99 on which the axially extending fins 102 of the valve are guided.

Fig. 2 shows a form of valve 38 used in commercial practice to time the flow of low pressure working fluid through the fluid lines 41, 42, 43, 44, enroute to and from the low pressure fluid chambers of the respective intensifiers 28, 29. The valve 38 includes a fluid motor comprising a vaned rotor 103 which drives through its shaft 104 and sprocket 105 a chain 106 trained about the sprocket 107 on the shaft 108 of worm 109 meshing with worm wheel 110 of cam shaft 113. Cam track 114 of cam shaft 113 is engaged with the cam followers 115 of stems 116, 117 for spool valves 118, 119. The spool valves 118, 119 regulate the flow of fluid through the valve 38. In the valve structure described, the flow of low pressure working fluid exhausting from the intensifiers energizes the fluid motor to actuate; the valves 118, 119 in time with the movement of the free pistons 53 in the respective pressure intensifiers 28, 29.

In the position of the parts shown in Fig. 2, low pressure working fluid 35 enters the valve 38 through the line 39 and valve port 122. In the illustrated position of valve 118 the low pressure working fluid will pass through valve chamber 123 and through both valve ports 124 and 125 respectively into lines 44, 41. Enroute to port 125 the fluid passes through valve chamber 126 and through the spool valve 119. Accordingly, the portions of the low pressure working fluid chamber 50 to the right of piston 53 in intensifier 29 and to the left of piston 53 in intensifier 28, as shown in Fig. 2, are placed under pressure of fluid entering through ports 66 and 63 respectively. Pressure of the low pressure working fluid on the face 56 of piston 53 in intensifier 29 and on the face 55 of piston 53 in intensifier 28 forces the respective pistons in the direction of arrows 120 in Fig. 2.

High pressure captive fluid 46 within the high pressure cylinders 54 of piston 53 in intensifier 29 and within the high pressure cylinders 57 of piston 53 in intensifier 28 will thus be pressurized in a ratio, of approximately six to one in the embodiment illustrated. The high pressure captive fluid is discharged respectively through tubes 60 and 62 in the direction of arrows 127 into isolator piston chamber 27 of intensifier 29 and isolator piston chamber 33 of intensifier 28, forcing the isolator piston 47 in chamber 27 to the left as shown in Fig. 2 and isolator piston 47 in chamber 33 to the right as shown in Fig. 1. The pressure on the pistons 47 may be as high as 12,000 to 15,000 p.s.i. in the particular embodiment illustrated.

Accordingly, the pumped fluid previously drawn into the chambers 27, 33 is placed under substantially equal high pressure and is forced out of the respective chambers 27, 33 in the direction of arrows 128 through respective check valves 92 to pressure ducts 23 and the well head shown in Fig. 1.

As the free pistons 53 move as aforesaid, spent low pressure working fluid respective in cylinders 50 at the left of piston 53 in intensifier 29 and at the right of piston 53 in intensifier 28 is discharged respectively through ports 64, 65 and hydraulic lines 42, 43 into ports 129, 142 of valve 38. The spent low pressure working fluid in port 129 travels through the valve chamber 131 at the left of spool valve 119 and through ducts 132 and 133 in the direction of arrows 135 and against the vanes 136 of the rotor 103 and thence out through duct 134 and fluid line 45 back to storage tank 36. Spent low pressure working fluid in port 142 travels through valve chamber 130 at the right of spool valve 118- and through duct 143 to commingle with the fluid in ducts 132, 133 for passage through the fluid motor and return to the storage tank 36.

The respective vanes 136 on the rotor 103 are received in pockets formed in the conventional check valves 137, 138 with which the valve 38 is provided. The check valves 137, 138 are connected by gearing (not shown) to the rotor 103 for rotation in timed relation thereto.

As the free pistons 53 move to the left and right in intensifiers 29, 28 respectively, the isolator pistons 47 in the isolator chambers 26 and 34 respectively are retracted or are drawn toward the end heads 49 and 51 of intensifiers 28, 29. This movement of the isolator pistons 47 draws into chambers 26, 34 fresh charges of fluid 13. For this purpose, valves 92 are closed and valves 88 are open and the fluid being pumped travels in the direction of arrow 139 to fill these chambers.

Rotor 103 and cam track 114 are so timed with respect to the stroke of pistons 53 that when the pistons 53 complete their stroke in one direction of reciprocation the cam 114 will have moved the spool valves 118, 119 to a position to reverse the direction of flow of low pressure Working fluid. At this'point in the cycle of the valve 38 the low pressure working fluid will be admitted to the respective cylinders 50 of intensifiers 28, 29 through ports 64, 65 to reverse the direction of piston movement. The respective isolator pistons 47 will now reverse their directions of movement and the previously closed check valve 88 opens and the previously open check valve 92 closes. The fluid line connections are such, however, that a constant intensified pressure is uniformly and continuously applied to the well head. Moreover, rotor 103 of valve 38 will continue to turn under the pressure of spent low pressure working fluid, admitted to valve 38 through the ports 124, routed by the spool valves 118, 119 through the ducts 132, 143 and 133 in the manner aforesaid.

Where, as in the specific embodiment of the invention herein described, the working fluid constitutes a substantially incompressible liquid, the lines 41-44 may optionally be provided with conventional gas pressure accumulators 144, as shown in Fig. 1. The accumulators will store low pressure motor actuating liquid in the pressure stroke of the piston 53 in quantities dependent on the initial gas pressure thereof. The gas pressures to which the respective accumulators are subject is so adjusted with respect to the liquid requirements of the fluid valve motor at maximum pressure requirements thereof that such additional quantities of liquid as may be required by the fluid motor 103 when the stroke of the piston 53 shortens at higher pressure requirements thereof will be made up from that increment of liquid which would, at a higher pressure, store in the accumulator. Thus, the accumulators balance the low pressure captive liquid requirement of the fluid motor to its output volume demand. On the exhaust stroke of piston 53 there is an excess quantity of spent low pressure working liquid in the system and stored in the accumulator and which will insure operation of the motor in valve 38 even if liquid has leaked therefrom. Accordingly, pistons 53 will not tend to drift down to the end of the cylinder 50 because of any loss of liquid volume therefrom.

Except for the high pressure of the pumped fluid 13 which is within isolator-chambers 26, 27, 33, 34, these being desirably fabricated with thickened walls to withstand the high pressure therewithin, the captive fluid 46 in the pumping portions of the device is confined within the high pressure cylinders formed by the tubes 60, 62 and the bores 54, 57 of the piston 53. Accordingly, if for any reason these high pressure cylinders burst or explode, the force of the resulting explosion will be substantially entirely absorbed and contained by the relatively low pressure fluid 35 and the cylinders 50.

Inasmuch as the pistons 53 are double acting and work against cushions of working fluid in the respective ends of the cylinder 50 in both directions of piston reciprocation, mechanical and fluid shocks are substantially eliminated in the intensifiers of the present invention.

In order to insure smooth operation of the isolator pistons 47 and preclude lodging of any foreign matter between the pistons and the isolator piston cylinders, a measured amount of high pressure captive fluid is desirably flushed between the pistons 47 and their cylinder Wall at the outward end of their travel in each reciprocation of the free floating pistons 53. For this purpose the respective pistons 53 are provided with axial bores of small cross section. The bores 145 are desirably disposed on the axis of reciprocation of the piston 53 and align with the pistons 146 fixed by bolts 141 in the respective end heads 49, 51. See Figs. 3 and 5.

The respective bores 145 and pistons 146 comprise fluid flushing pumps to force a measured amount of working fluid through the cross ducts 147 and check valve chambers 148 through the check valves 149 into at least one of each pair of bores 54, 57.

The flushing pumps add a slight excess of working fluid to the isolator chambers 26, 27', 33, 34 in each cycle of the intensifiers, so that this excess of fluid will flush past the respective isolator pistons 47 in each reciprocation thereof on reaching the outward end of their stroke. The flow of flushing fluid cleans out and discharges such foreign matter and gas or air as may separate from the fluid on the captive fluid side of the pistons. Such foreign matter may otherwise lodge against the walls of the cylinder 68 to interfere with the operation of the pistons 47.

For example, as illustrated in Fig. 5, as piston 53 moves toward the left, bore 57 will tend to fill with fluid 35 drawn thereinto through the tube 62 from the isolator chamber communicating therewith. However, as flushing pump piston 146 enters bore 145 an additional charge of fluid 35 equal to the amount of fluid displaced from bore 145 will be forced through cross duct 147 and through check valve 149 in the direction of arrow 152 into bore 57. In effect the isolator piston 47 in, the chamber with which tube 62 communicates will not retreat quite as far as it otherwise could. Accordingly, in the last increment of movement of piston 53 toward the right the excess fluid behind the isolator piston 47 will flush past and through the piston to commingle with the pumped fluid in the isolator chamber and carry with it any foreign matter, etc. that might otherwise jamb the piston. Both ends of piston 53 are provided with flushing pumps as indicated in Fig. 5.

Springs 78 in isolator piston 47 are set at a pressure such that plate valves 77 may open to bypass such flushing fluid as is unable to flush between the chevron rings 73 and the isolator cylinder wall in the time allowed.

I claim:

1. A pressure intensifier comprising a cylinder for relatively low pressure fluid, a member mounted within said cylinder for free reciprocating movement axially thereof, said member being provided with axial bores opening from both ends thereof, corresponding tubes relatively fixed in both end walls of said cylinder and extending respectively into corresponding bores of the axially movable member, said tubes and bores together constituting high pressure fluid cylinders and pistons, means for imposing the pressure of the fluid in said high pressure fluid cylinders on an energy absorbing medium, and means for selectively subjecting the respective ends of the reciprocating member to a relatively low pressure fluid to cause reciprocating movement thereof, the movement of said member in one direction pressurizing fluid in one set of bores and tubes and movement of said member in the opposite direction pressurizing fluid in another set of tubes and bores.

2. The device of claim 1 in further combination with a chamber communicating with ahigh pressure fluid cylinder, means for selectively admitting to and releasing from said chamber pumped fluid to be pressurized therein, and isolator means within said chamber to isolate said high pressure fluid from the pumped fluid.

3. A pressure intensifier comprising a cylinder for relatively low pressure fluid, a member mounted within said cylinder for free reciprocating movement axially thereof, said member being provided with axial bores, tubes relatively fixed in the end walls of said cylinder and extending within the bores of the axially movable member, said tubes and bores together constituting high pressure fluid cylinders and pistons, means for imposing the pressure of the fluid in said high pressure fluid cylinders on an energy absorbing medium, and means for selectively subiecting the respective ends of the reciprocating member to a relatively low pressure fluid to cause reciprocating movement thereof, in further combination with a chamber communicating with a high pressure fluid cylinder, means for selectively admitting to and releasing from said chamber pumped fluid to be pressurized therein, and isolator means within said chamber to isolate said high pressure fluid from the pumped fluid, the pumped fluid being characterized by granular foreign matter suspended therein, said isolator chamber comprising a cylinder, said isolator means comprising a piston mounted for free reciprocation in said cylinder, and means for periodically flushing past said isolator piston a measured quantity of fluid from said high pressure cylinder whereby to clear the piston of any such foreign matter as may tend to lodge between the isolator piston and isolator cylinder.

4. The device of claim 3 in which said flushing means comprises a fluid pump comprising a cylinder formed in said, reciprocating member and a fixed pump piston mounted on an end wall aforesaid and telescopically receivable in said flushing pump cylinder, said pump cylinder having a passage communicating with said high pressure cylinder whereby in the movement of said freely reciprocating member toward said pump piston an additional quantity of fluid is added to the high pressure cylinder to be flushed past said isolator piston as aforesaid.

5. The device of claim 3 in which said means for admitting and releasing pumped fluid with respect to said chamber comprises a check valve having a seat, said valve having a valve facing comprising an elastomer having a surface pattern including ribs and grooves, foreign matter in said pumped fluid being swept into said grooves in the course of valve closing to leave the ribs thereof in intimate sealing contact with the valve seat.

6. In a pressure intensifier, the combination of a low pressure cylinder having end walls, a free floating piston in said cylinder, said piston having chambers respectively opening to opposite ends of said piston and. comprising high pressure cylinders, tubes mounted in'the end walls of the low pressure cylinder and extending. into said chambers and communicating therewith to. further constitute said high pressure cylinders, the areaof an exposed face of said piston being materially larger than the effective cross sectional area of said high pressure cylinder whereby fluid pressure exerted on apiston face is multiplied in said high pressure cylinder, first means for imposing the pressure of the fluid in said high pressure cylinders on an energy absorbing medium and second means for selectively subjecting the respective faces of the floating piston to relatively low pressure fluid to reciprocate the piston in the cylinder.

7. The device of claim 6 in which said first means comprises isolator chambers in the respective ends of said low pressure cylinder and communicating with the said high pressure tubes whereby to pressurize said isolator chambers to the same pressure as the high pressure cylinders, isolator means in said isolator chambers and means for admitting to and releasing from said chambers at the opposite sides of said isolator means from said high pressure cylinders pumped fluid to be pressurized, and check valve means incorporated rtherein, said check valve means being responsive to actuation of said isolator means by said high pressure fluid to automatically admit and discharge said pumped fluid.

8. A well pressurizing system comprising plural intensifiers according to claim 7, together with valve means for alternately supplying low pressure fluid to the opposite ends of said free floating piston in timed relation to the movement thereof.

9. The device of claim 8 in which said valve means comprises valve members, and a fluid motor coupled to said valve members for the actuation thereof, said fluid motor being in the path of fluid flow from said intensifier for energization by said flow. Y

10. In the combination with a pressure intensifier having a low pressure working fluid chamber and a high pressure captive fluid chamber and floating piston means defining said chambers and subject to low pressure working fluid to pressurize captive fluid in the high pressure chamber, an isolator cylinder communicating with said high pressure chamber, an isolator piston in said cylinder to one side of which said captive high pressure fluid is exposed, means for admitting and releasing to and from the other side of said isolator piston a pumped fluid containing foreign matter in suspension, of means for flushing past said isolator piston captive high pressure fluid which will commingle with said pumped fluid, said means comprising a fluid pump, means responsive to movement of said floating piston to actuate said pump and connections from said pump to said high pressure chamber to add a measured quantity of Working fluid to the high pressure chamber to provide an excess of high pressure captive fluid in said high pressure chamber for flushing purposes. I

11. The device of claim 10 in which said free-floating piston is provided with a bore, said low pressure chamber being provided with a tube registering with said bore, said tube and bore together comprising said high pressure chamber, said piston being provided With a second bore communicating with the bore first mentioned, said low pressure chamber being provided with a piston registering with said second bore, said second bore and piston constituting said pump and effective upon movement of said free floating piston to a position in which said pump piston enters said second bore to force low pressure working fluid accumulated therein into said high pressure chamber.

12. The device of claim 11 in which said flushing pump includes a check valve which permits flow of fluid in said duct only in a direction toward said high pressure chamber.

13. In a device of the character described, a valve for controlling flow of fluid in which foreign matter is in suspension, a valve seat, said valve comprising an elastomer valve facing having a surface pattern of ribs and grooves cooperating with said valve seat, said grooves being interrupted by ribs to provide partially enclosed pockets exposed only at said valve facing and in which foreign matter in said fluid may lodge in the course of valve closing movement to insure a tight seal of the ribbed portions of said facing against said seat.

14. The device of claim 13 in which the pattern of said ribs and grooves of said facing further comprises concentric annular ribs and transverse ribs partially enclosing said groove pockets.

15. An isolator piston of the character described comprising an annulus having chevron packing rings thereabout and a spring biasing said chevron packing rings in pressure contact, said annulus having an end wall with a flushing port, a valve over said port and spring means biasing said port to closed position subject to being opened by flushing pressure at the side of the port opposite the spring.

References Cited in the file of this patent UNITED STATES PATENTS 2,125,463 Ryan Aug. 2, 1938 2,318,782 Jorgensen May 11, 1943 2,624,284 Straub Jan. 6, 1953 2,770,443 Rand Nov. 13, 1956 FOREIGN PATENTS 323,827 Great Britain Jan. 16, 1938 744,589 France Jan. 26, 1933 

